Transmission line hangers are used to support transmission lines. Transmission lines are supported by attaching them to supporting structures by transmission line hangers. The most extensive use of hangers is in connection with coaxial cables, such as those disclosed in U.S. Pat. No. 5,334,051 (Devine et al.) and 5,167,533 (Rauwolf). Coaxial cables are extensively used for carrying a variety of electromagnetic signals. In most uses, the cables need to be attached to a supporting structure along most of their lengths.
Transmission line hangers are also used for supporting waveguides which carry electromagnetic signals from transmitting or receiving equipment in an equipment shelter to an antenna mounted on a tall tower. A large number of hangers are required to support a waveguide beneath a horizontal waveguide bridge extending between the shelter and the base of the tower and to support the waveguide on the tower as the waveguide extends upwardly to the antenna. An even larger number of hangers are required where separate waveguides extend to several antennas on a signal tower. Commercially available waveguides have a variety of cross-sectional shapes. For example, a variety of waveguide shapes are disclosed in U.S. Pat. Nos. 3,822,411 (Merle) and 4,047,133 (Merle).
A typical hanger for elliptical-shaped waveguides includes a generally U-shaped clip adapted to be attached to a support member on the bridge or the tower by a bolt extending through a hole in the support member and held in place by a nut and lock washer. After the hangers have been attached to the support members, the waveguide is strung along the bridge, up the tower and clamped between the legs of each U-shaped hanger by tightening a clamping screw which extends between the legs. A considerable amount of installation time is required, first to attach the large number of hangers to the bridge and the tower and then to clamp the waveguide within the hangers. In addition, a large amount of auxiliary hardware (e.g., screws, bolts, nuts and washers) is required along with the hangers themselves.
A spring hanger system for supporting a VHF circular waveguide is disclosed in U.S. Pat. No. 4,654,612 (Smith). A variety of prior hangers for microwave transmission lines are disclosed in Andrew Corporation Catalog #36. An improved waveguide hanger is disclosed in U.S. Pat. No. 4,763,132 (Juds et al.). The waveguide hanger disclosed in the Juds et al. patent is in the form of a resiliently yieldable and generally U-shaped clip 1, illustrated in FIG. 1, that is adapted to be slipped over an elliptical waveguide and snapped into a supporting member. The clip includes a hinge portion 2 that extends between the legs 3 of the clip 1.
Another cable hanger is disclosed in U.S. Pat. No. 5,393,021 (Nelson). As illustrated in FIG. 2, the cable hanger 200 disclosed there includes a hinge section 320, a cable retention section 340, and a structure attachment section 360 having two locking members 580 that each include a pair of concave locking barbs 600.
Cable hangers that include hinges can only accommodate a limited range of cable diameters. The maximum cable diameter accepted by such cable hangers is limited by the maximum circumference of the cable retention section.
Prior cable hangers, such as Nelson and Juds et al., also place the cable retention section close to the attachment section. Thus, the attachment section is traditionally short in length. This makes the attachment section rigid and non-compliant which makes installation of such hangers difficult especially where a large diameter cable is being installed on a tower or where the weather conditions limit manual dexterity, e.g., cold weather. In such situations, tools may be required to squeeze the hanger into the tower aperture. The use of tools is undesirable especially where a cable is being installed on a high tower.
Furthermore, some prior hanger designs do not adequately prevent longitudinal movement of the cable with respect to the hangers. Hangers without mechanisms for penetrating or biting into the cable jacket can not prevent longitudinal movement of the cable because the frictional coefficient between the metal hanger and the plastic cable jacket is very low, since the polyethylene typically used for cable jackets is a soft material that has an inherent lubricant quality. In addition, the cable jacket can "cold flow" which reduces the holding force of the cable hanger over time, resulting in cable slippage.
The installation of transmission line hangers is often a difficult and time-consuming operation because of the large amount of auxiliary hardware required to install some prior hangers. Therefore, there is a continuing need for efficient, inexpensive hangers and for improved methods of installing them. The present invention addresses these needs by providing a transmission line hanger that can be easily and efficiently installed, is expandable to accommodate a large number of transmission line diameters, and can reduce longitudinal movement of the transmission line within the hanger, and is inexpensive to produce.